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Simulating sundials

Calcad approach using two shadow points is a quick and easy way to define the layout of a sundial … provided that you know exactly where you are going to install it. But what if you have the choice of several sites? For example, suppose you want a sundial that you'll consult mainly in the afternoon. Should you site it vertically on the side or the front of your house or horizontally in the middle of the lawn? You can simulate the three possibilities and choose the one that gives the most useful readings.

To simulate a sundial, you first enter its details in the appropriate tabs:
o   Dial: enter the side(s) of the dial and the height of the provisional gnomon tool (the other values may be added later)
o   Place: enter the complete localization of the sundial. Values within 1 degree are sufficiently accurate for simulation (when you have decided on the position, the real measurement of the 2 shadow points will allow you to calculate an accurate layout)
o   Point 1 and Point 2: optionally (if you are going to use the Simulate button) indicate two different moments when the plane of the dial will be lighted

Then, in the Other tab, enter the three angles that define the orientation of the sundial:

o   Declination measures the compass orientation: the angle between the sundial and the meridian. The declination is 0 if the sundial faces due south, and values can range from 0 to 180° east or west. You can get a sufficient estimation using a simple compass
o   Inclination measures the slope of the dial with respect to the surface of the Earth. The inclination is 0° for a horizontal dial (facing directly upwards) and 90° for a vertical dial (facing the horizon). For intermediate slopes, a protractor and a spirit level will allow you to get a sufficient estimation
o   Rotation measures on the sundial the angle between the x axis and an horizontal line of the dial (-180 to 180°). This will normally be 0, and the horizontal lines of the sundial will be represented horizontally on the diagram, unless you want to follow the example of Mr. Slope

Then, still in the Other tab, you can:
o   Press the Draw button or type Ctrl + K to draw the dial directly (this is in fact the classical method used by other sundial software)
o   Press the Simulate button or type Ctrl + L to compute the position of the shadow points and then use them to compute the dial. In this case, you may need to modify the time of the point(s) so that their shadow falls inside the dial

If the simulation succeeds, go to the sundial layout options.

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